Inorg. Chem. 1983, 22, 1054-1059
1054
Contribution from the Department of Chemistry, State University of New York at Buffalo, Buffalo, New York 14214
Transition-Metal Complexes of Organoaluminum Phosphides. Synthesis, Characterization, and Crystal and Molecular Structure of Cr(CO)5[PPh2Al(CH2SiMe3)2*NMe3] CLAIRE TESSIER-YOUNGS, CLIFFORD BUENO, 0. T. BEACHLEY, JR.,* and MELVYN ROWEN CHURCHILL* Received December 29, 1981
The reactions of organoaluminum phosphides with a variety of transition-metal carbonyl complexes containing labile ligands have been investigated. The reaction of Cr(CO)5NMe3with (Me3SiCH2)2AlPPh2 in benzene solution leads to the formation of Cr(C0)5[PPh2A1(CH2SiMe2)2.NMe3], a fully characterized new compound. An X-ray structural study has identified separated by normal van der Waals distances, in the discrete isolated molecules of Cr(CO)5[PPh2A1(CH2SiMe3)2.NMegl, monoclinic crystal space group P21/n with a = 11.839 (4) A, b = 18.517 ( 5 ) A, c = 16.158 (4) A, @ = 90.32 (2)", and p(ca1cd) = 1.20 g/cm3 for 2 = 4 with molecular weight 637.82. Diffraction data were collected with a Syntex P21 diffractometer,and the structure was refined to RF= 6.4% for all 4948 reflections. There are no abnormally short intermolecular contacts. The unusual features identified in the investigation are the long bond distances for AI-P of 2.485 (1) A and Cr-P of 2.482 (1) A. The AI-N bond seems to be normal. The geometry about the tetrahedrally coordinated phosphorus atom is decidedly irregular. Similarly, the aluminum atom has a rather distorted tetrahedral environment. The reaction with anhydrous HBr leads to the formation of Cr(CO)5PPh2H,Br3AlNMe3,and of Cr(CO)5[PPh2A1(CH2SiMe3)2.NMe2] SiMe,. A likely path for this r ction involves the initial cleavage of the long P-A1 bond. In attempts to find other preparative reactions to compounds with a k P - A l bond sequence, the related reactions of Cr(C0)5L (L = CO, CH3CN,THF) with R2AIPPh2(R = Me, Et) were studied but the desired compounds were not formed. Available data suggest that the labile ligand on chromium was attacked by the aluminum-phosphorus reagent.
Introduction The diphenylphosphido group has been recognized as an excellent bridging ligand in many transition-metal and main-groupmetal complexes. It has served as a building block for transition-metal clusters and main-groupelement polymers. However, there is only one previous example as a well-defined compound in which the phosphido group bridges a transition metal and main-group-element moiety. The novel compound' Cr(CO)5PPh2B(NMe2)2was prepared from Cr(CO),(THF) and PPh2B(NMe2)2. Since there are no examples of fully characterized compounds in which the phosphido group bridged a transition-metal and a main-group organometallic moiety, the goal of our research was the synthesis of a complex with the formula Cr(CO),(PR2A1R2). A logical route to a compound of this type involves the reaction of a transitionmetal complex containing a labile ligand with a reactive and basic main-group organometallic phosphide. However, all known compounds of the type R2AlPR2 exist as dimers or trimer^^.^ with coordinatively saturated aluminum and phosphorus atoms. Consequently, a method had to be found to provide an aluminum-phosphorus species that could react as a Lewis base with Cr(C0)5. For comparison, the boron compound,' PPh2B(NMe2)2,used to prepare the complex with the Cr-P-B bond sequence, is a monomer and has a basic phosphorus atom. There are two experimentally attractive ideas for generating a monomeric aluminum-phosphorus species with a three-coordinate phosphorus atom. Bulky substituents on aluminum might decrease the stability of an associated species and enable a monomeric RzAlPR2species to be available for reaction. However, the substituents on aluminum must not reduce the basicity of the phosphorus atom. Another way to obtain a potentially reactive aluminum-phosphorus compound is to disrupt an associated species with a Lewis base. Some 'H N M R spectral data and some reaction chemistry2v3suggest that dimers can be cleaved, often reversibly, with a Lewis base to form :Pr'2-A1R2.base. The (1)
NBth, H.; Sze, S. N. 2.Naturforsch., B Anorg. Chem., Org. Chem. 1978, 338, 1313.
known lability of an amine or other nitrogen and oxygen bases for a Cr(CO),L complex would provide the necessary Lewis base to distrupt the aluminum-phosphorus dimer as well as produce the reactive Cr(CO), moiety. In this paper was focus on the reactions of Cr(CO),NMe, with organoaluminum diphenylphosphides in hydrocarbon solvents. The first example of the desired class of compounds, Cr(CO);[PPh2A1(CH2SiMe3)2.NMe3], has been prepared and characterized by analysis, spectroscopic methods, and an X-ray structural study. The choices of the specific organoaluminum phosphide and the transition-metal derivative are crucial for the successful synthesis of the desired type of compound. The reactivity of (Me3SiCH2)2A1PPh2,which exists as a mixture of monomer and dimer species in benzene s ~ l u t i o nis, ~compared with that of Me2A1PPh2, and Et2A1PPh2,6which are dimers. The reactions of Cr(CO)s(THF), Cr(CO)5(CH3CN), and Cr(C0)6 with [R2A1PPh2], (R = Me, Et) are also described, but they do not provide good routes to the desired class of compounds because the labile chromium ligand reacts with the aluminum phosphide under reaction conditions. Experimental Section Materials. All compounds described in this investigation were manipulated in a vacuum line or a purified argon atomosphere. Reagent grade solvents were employed. Aliphatic hydrocarbon solvents were treated with concentrated sulfuric acid to remove unsaturated compounds. All hydrocarbon solvents were refluxed with and stored over sodium and then vacuum distilled from phosphorus pentoxide immediately prior to use. Ethers were refluxed with and vacuum distilled from sodium-benzophenone ketyl. The preparations of Me2AlPPh2: EtzAlPPh2,6 (Me3SiCHz)2AlPPhz,4 Cr(CO),NMe,,' and Cr(CO)5(CH3CN)8have been described elsewhere. As a final purification, Cr(CO),NMe3 and Cr(CO)5(CH3CN)were sublimed at room temperature under vacuum. Even though these chromium compounds possess considerable air stability as solids, they were handled as air- and water-sensitive materials. The waters of hydration Tessier-Youngs, C. Ph.D. Thesis, State University of New York at Buffalo, 198 1. Coates, G. E.; Graham, J. J . Chem. SOC.1963, 233. ( 6 ) Johnson, A. W.; Larson, W. D.; Dahl, G. H. Can. J . Chem. 1963, 43,
(4)
(5)
1338.
Coates, G. E.; Green, M. L. H.; Wade, K. "Organometallic Compounds", 3rd ed.;Methuen: London, 1967; Vol. 1, Chapter 3. (3) Mole, T.; Jeffrey, E. A. 'Organoaluminum Compounds"; Elsevier: New York, 1972; Chapter 5. (2)
0020-166918311322-1054301SO10
(7) (8)
Wasserman, H.J.; Wovkulich, M. J.; Atwood, J. D.; Churchill, M. R.
Inorg. Chem. 1980, 19, 2831. Connor, J. A.; Jones, E. M.; McEwen, G. K. J. Orgummet. Chem. 1972, 43, 357.
0 1983 American Chemical Society
C r ( C O ) 5 [PPh2A1(CH2SiMe3)2.NMe3] in M e 3 N 0 and NEt4C1, starting materials for the preparation of Cr(C0)5NMe3and Cr(CO)s(CH3CN), were removed by heating at 110 OC under vacuum. Due to the extreme sensitivity to oxygen and water of the aluminum-containing reaction mixtures, most reactions were carried out in break-seal tubes, a 25 X 3 cm tube equipped with a constricted side arm and a side-arm break-seal. The reagents and solvents were loaded through the constricted side arm, and then it was sealed under vacuum. Analyses. Microanalytical analyses were peformed by Pascher Microanalytisches Laboratorium, Bonn, Germany. The (trimethylsily1)methyl deriatives were analyzed for hydrolyzable CH2SiMe3groups by measuring the SiMe, evolved upon hydrolysis with dilute HNO,. SiMe, was separated from all other volatile componentns by passage through two -78 OC traps and into a -196 OC trap and measured by using a known volume in the vacuum line. The purity and identity of the SiMe, were verified by vapor pressure measurements and its infrared spectrum. Infrared Spectra. Infrared spectra of Nujol mulls were recorded by means of a Perkin-Elmer Model 457 spectrometer using CsI plates and referenced to polystyrene. Absorption intensities are reported with the abbreviations w (weak), m (medium), s (strong), vs (very strong), and sh (shoulder). Nuclear Magnetic Resonance Spectra. The ‘H NMR spectra were recorded at 90 MHz with a Varian Model EM-390 spectrometer. Chemical shifts were measured from solvent signals or residual proton signals of deuterated solvents and referenced to tetramethylsilane as T = 10.00. The multiplicity of an N M R signal is reported with the abbreviations s (singlet), d (doublet), m (multiplet), and b (broad). All N M R tubes were sealed under vacuum. Synthesis of Cr(CO)s[PPh2Al(CH2SiMe3)2.NMep]. The complex Cr(CO)S[PPh2A1(CH2SiMe3)2.NMe3] was prepared by the reaction of (Me3SiCH2)2A1PPh2 and Cr(CO),NMe2 in benzene. a break-seal tube containing 0.58 g (1.5 mmol of (Me3SiCH2)2AlPPh2,0.58 g (2.3 mmol) of Cr(CO)SNMe,, and 10 mL of benzene was prepared. The reaction mixture was stirred for 48 h. After 12 h, a distinct color change had occurred; the solution had changed from bright orange to yellow. The tube was opened under vacuum, and the solution was filtered into a flask. Pentane (5 mL) was vacuum distilled into the flask; the resulting solution was kept at 0 OC for 12 h, and 0.40 g (42%) of yellow crystals of Cr(C0)s[PPh2Al(CH#iMe3)2.NMe3] (mp 109-1 11 “C) was isolated by filtration. A second crop of crystals (0.15 g, 16%) was obtained by removing the solvent by vacuum distillation, dissolving the residue in a minimum amount of pentane, and cooling the solution to -20 OC. The combined crystals were subjected to high vacuum for 12 h (until no more yellow Cr(C0)sNMe3 condensed in the trap) and then recrystallized from pentane. Mp: 110-111 OC. Anal. Calcd: C, 52.73; H, 6.48; N, 2.20; P, 4.86 (Me,Si, 2.00 mol/mol). Found: C, 52.27; H, 6.30; N, 2.02; P, 4.99 (Me@, 1.97 mol/mol). lH NMR, (benzene-d6): T 2.23 (t, J = 9 Hz, Ph), 3.03 (m, Ph), 8.52 (s, NCH,), 9.99 (s, SiCH,), 10.02 (s, SiCH,), 10.05 (s, SiCH,), 10.19 (s, A1CH2), 10.63 (s, A1CH2), 10.73 (d, AlCH2). IR (cm-I): vco 2069 (m), 1970 (m, sh), 1922 (vs, b). The reaction of equimolar quantities of (Me3SiCH2)2A1PPh2and Cr(CO),NMe, was followed by ’H NMR technqiues. About 0.4 mL of benzene-d6 was vacuum distilled at -196 OC onto 0.035 g (0.91 mmol) of (Me3SiCH2),A1PPh2 and 0.023 g (0.91 mmol) of Cr(CO)SNMe3contained in an NMR tube. The tube was sealed at -196 OC under vacuum and kept frozen until just prior to recording the first ‘H NMR spectrum. The spectrum was again recorded at intervals of 2,9.5,21.0, 25.5,35.0,46.5, and 72 h. After 9.5 h the bright orange solution had lightened considerably, and by the end of the experiment a nearly colorless solution was present. These spectra are discussed in the Results and Discussion. Reaction of Cr(CO)5[PPh2Al(CH2Sie3)2.NMe3] with Anhydrous HBr. The nature of the reaction of Cr(C0)s[PPh2Al(CH2SiMe3)2-NMe3]with HBr was studied by using ‘HN M R techniques. A quantity of HBr was measured on the vacuum line and distilled onto a benzene-d6 solution of a known mass of Cr(CO)S[PPh2A1(CH2SiMe3)2-NMe3] contained in a bulb with a side-arm NMR tube. Reaction was allowed to take place for 8 h. The resultant solution was poured into the N M R tube, the tube was frozen to -196 OC to ensure that no volatile components were lost, the tube was sealed, and the IH N M R spectrum was recorded. The reaction of a benzene-d6 solution of Cr(CO)S[PPh2Al(CH2SiMe3)2.NMe3]with HBr in a 1:3.2 mole ratio caused the light
Inorganic Chemistry, Vol. 22, No. 7, 1983 1055 Table I. Data for the X-ray Diffraction Study of (Oc),Cr[ PPh, AI(CH, SiMe,),.NMe, ] (A) Crystal Parameters 3542 (2) monoclinic V, A3 P2,In 2 4 11.839 (4) mol wt a, A 637.82 18.517 (5) p(calcd), g cm-3 b, A 1.20 16.158 (4) M , cm-’ e, A 5.1 P, deg T, “C 24 90.32 (2) (B) Measurement of Data diffractometer: Syntex P2, radiation: Mo K a (X = 0.710 730 A) monochromator: pyrolytic graphite (equatorial) reflcns measd: +h, +k, r l for 3.0” < 26 < 46.0’ scan type: e-2e scan speed, deg/min: 4.5 scan range, deg: symmetrical, [2.0 + A(&, - a 2 ) ] bkgd: at beginning and end of scan; each for ‘I2 scan time total measurement: 5590 reflections; yielding 4948 unique data
cryst syst space group
yellow solution to become virtually colorless. The ‘H NMR spectrum showed absorbances for Cr(CO)5PPh2H, SiMe,, and Br,Al.NMe, ( r = 8.44). A reaction mixture with a mole ratio of Cr(CO)s[PPh2Al(CH#iMe3)2.NMe3]:HBr of 1:4.8 produced a nearly colorless solution, a white solid, a green solid, and some CO. The IH N M R spectrum of the resulting solution showed lines consistent with the presence of Cr(CO)5PPh2H and SiMe,. Crystallographic Studies. The crystal used for X-ray study was obtained by dissolving Cr(CO)5[PPh2A1(CH2SiMe3)2.NMe3] in a minimum of pentane and then cooling to 0 OC for 5 h. After the crystals were separated by filtration, a crystal (maximum orthogonal dimensions 0.47 X 0.25 X 0.20 mm) was selected in an argon-filled drybox and then sealed in a thin-walled glass capillary. The crystal was mounted on a Syntex P21 automated four-circle diffractometer. The unit cell parameters and the orientation matrix were determined as described previously: data collection was peformed by using the 8-28 scan method (details see Table I). Data were corrected for Lorentz and polarization factors and for absorption and were reduced to IFoI values; any reflection with I,,,, < 0 had its IFo] value reset to zero. Solution and Refinement of the Structure. All calculations were performed by using our in-house Syntex XTL structure determination system.I0 The analytical scattering factors of neutral atoms were corrected for the real (Af’) and imaginary (iAf”) components of anomalous dispersion.’l The function minimized during the leastsquares refinement process was x:w(lFol - IFc1)2,where the weights ( w ) are obtained from counting statistics modified by an ingnorance factor (p) of 0.02. The structure was solved by direct methods using M U L T A N ~and ~ was refined by difference-Fourier and full-matrix least-squares refinement techniques to RF = 6.4%, RwF= 5.7%, and GOF = 1.6313 for all 4948 independent reflections (none rejected) or RF = 5.0%, R w p = 5.4%, and GOF = 1.71 for those 4134 reflections with IFoI > 30(lFoI). The N0:NV ratio was 4948:352 or approximately 14.1:l. All hydrogen atoms were included in calculated positions with d(C-H) = 0.95 A;14 these positions were updated but not refined. Final positional parameters appear in Table 11. Anisotropic thermal parameters are collected in Table 111-S (supplementary data). Reaction of Cr(C0)5NMe3 with Et2AlPPh2 in Toluene. Cr(CO)SNMe3 (0.530 g, 2.11 mmol) and Et2AlPPh2 (0.550 g, 2.03 mmol) were stirred in 10 mL of toluene at r c “ temperature for 12 h in a break-seal tube. No change in the reaction color was observed. The tube was then heated at 70 OC for 3 h. Decomposition of Cr(CO)SNMe, occurred, producing Cr(C0)6 and a small amount of Churchill, M. R.; Lashewycz, R.A,; Rotella, F.J. Inorg. Chem. 1977, 16, 265.
“Syntex XTL Operations Manual”, 2nd ed.;Syntex Analytical Instruments: Cupertino, CA, 1976. ‘International Tables for X-ray Crystallography”; Kynoch Press: Birmingham, England, 1974; Vol. 4, pp 99-101, 149-150. Germain, G.; Main, P.;Woolfson, M. M. Acta Crystallogr., Sect. A 1971. 427. 368
observations; NV< number of variables. Churchill, M. R.Inorg. Chem. 1973, 12, 1213.
1056 Inorganic Chemistry, Vol. 22, No. 7, 1983
Tessier-Youngs et al.
Table 11. Fractional Coordinates for Atoms in the (OC),Cr[PPh,AI(CH, SiMe,),.NMe,] Molecule atom
X
Y
Z
0.002 86 (4) 0.293 29 (8) 0.106 01 (7) 0.423 39 (10) 0.533 54 (8) 0.253 62 (22) 0.129 31 (28) 0.220 86 (31) 0.237 30 (39) 0.161 79 (51) 0.070 36 (44) 0.052 92 (33) 0.022 42 (26) -0.078 89 (29) -0,136 12 (35) -0.092 77 (41) 0.006 67 (40) 0.064 03 (32) 0.496 30 (41) 0.313 02 (42) 0.530 20 (43) 0.604 27 (34) 0.53295 (41) 0.622 68 (30) 0.362 41 (29) 0.388 79 (28) 0.358 07 (32) 0.176 00 (38) 0.205 50 (46) -0.057 13 (30) 0.125 02 (32) -0.080 55 (31) -0.113 42 (29) 0.061 83 (28) -0.094 37 (26) 0.196 31 (25) -0.132 24 (24) -0.181 80 (22) 0.094 16 (24)
0.343 03 (3) 0.263 05 (5) 0.246 99 (4) 0.098 42 (6) 0.356 32 (6) 0.325 92 (15) 0.173 63 (17) 0.177 08 (20) 0.12421 (27) 0.068 80 (27) 0.064 61 (23) 0.116 79 (20) 0.199 37 (18) 0.225 73 (21) 0.19029 (27) 0.128 35 (27) 0.100 52 (22) 0.135 87 (19) 0.126 74 (29) 0.031 39 (24) 0.051 63 (29) 0.360 94 (25) 0.449 58 (25) 0.300 57 (26) 0.176 42 (19) 0.320 84 (21) 0.342 65 (23) 0.290 38 (29) 0.395 22 (26) 0.387 75 (20) 0.408 77 (20) 0.407 13 (21) 0.273 42 121) 0.308 45 (21) 0.418 47 (17) 0.450 13 (16) 0.445 67 (17) 0.23002 (16) 0.291 35 (19)
0.019 61 (3) -0.122 06 (6) -0.055 87 (5) -0.112 08 (8) -0.061 72 (6) -0.222 43 (16) 0.019 50 (20) 0.073 86 (22) 0.134 35 (26) 0.141 72 (30) 0.089 42 (32) 0.029 29 (24) -0.135 88 (19) -0.166 77 (22) -0.229 72 (27) -0.262 66 (27) -0.232 77 (26) -0.17040 (23) -0.015 09 (31) -0.086 16 (34) -0.177 10 (34) 0.041 05 (25) -0.105 76 (30) -0.131 06 (25) -0.170 11 (22) -0.047 36 (21) -0.268 17 (24) -0.281 27 (26) -0.195 15 (29) -0.076 49 (24) 0.020 17 (24) 0.081 96 (24) 0.024 83 (20) 0.120 32 (24) -0.13191 (19) 0.025 35 (22) 0.122 45 (20) 0.03093 (17) 0.184 22 (17)
green material. Et2AlPPh2was isolated unchanged from the toluene solution. Reactions of Cr(CO),(CH,CN) with Organoaluminum wosphides. (a) With Me2AIPPh2. A mixture of 0.235 g (1.01 mmol) of Cr(CO),(CH,CN) and 0.244 g (1.01 mmol) of Me2AlPPh2 (in 5 mL of diethyl ether) was stirred at room temperature for 20 days. The initial bright yellow solution and the white solid were slowly replaced by a pale orange solution and a pale yellow solid. The ether and a trace of unreacted Cr(CO)5(CH3CN)were removed by vacuum distillation, yielding 0.40 g of a pale yellow powder. Mp data: 175 OC, darkens; 187 OC, melts to a red liquid. IR (cm-I): vco 2075 (m), 1975 (m), 1938 (sh), 1915 (vs); vCcN 1601 (m). This compound had very low solubility in both hydrocarbon and ether solvents. (b) With Et2AIPPh2. A mixture of 0.636 g (2.73 mmol) of Cr(CO),(CH,CN) and 0.737 g (2.73 mmol) of Et2AlPPh2(in 5 mL of diethyl ether) was stirred for 2 h. A tan solid (0.659 g) precipitated and was isolated by filtration. Mp data: 148 OC, darkens; 160-162 OC, melts to a red liquid. IR (cm-I): vCEN 2156 (w); vco 2070 (m), 1980 (m, sh), 1939 (s, sh), 1909 (vs); v-N 1601 (m). This compound had low solubility in both hydrocarbon and ether solvents. Reaction Of C t ( C O ) 6 With M@PPhp A break-seal tube containing 0.529 g (2.18 mmol) of Me,AIPPh,, 0.602 (2.74 mmol) of Cr(C0)6, and 10 mL of toluene was heated at 140 OC for 22 h. The reaction mixture consisted of a brown solid and a brown solution after cooling to room temperature. The tube was opened under vacuum, the evolved carbon monoxide (0.501 mmol, 23%) was measured, and the reaction mixture was extracted several times with the toluene. After the volatile components were removed on the vacuum line, a brown residue remained. Virtually all the expected excess Cr(C06 (0.1342 g, 0.53 mmol) was separated from the volatile components. The brown residue was extracted several times with 10 mL of hexane. After removal of solvent by vacuum distillation a small amount of a sticky yellow material was obtained. Attempts to crystallize this material from hexane were unsuccessful. 'H N M R (toluene-d8): T 2.75 (m, Ph),
3.00 (m, Ph), 9.74 (s, AlCH3). IR (cm-I): vco 2075 (m), 2023 (w), 1977 (m), 1930 (vs), 1898 (s, sh). Similar results were obtained by varying the reaction time and temperature (1 10-140 "C). Reaction of Cr(CO),(THF) with Et2AIPPhP A solution of 0.710 g (3.23 "01) of Cr(C0)6 in 40 mL of THF was irradiated undr argon for 34 h. The resultant orange solution (under argon) was poured into a two-neck flask. A solution of 0.881 g (3.26 mmol) of Et2AlPPh2 in 5 mL of T H F was prepared in a tube with a Teflon stopcock, and the tube was attached to the flask containing Cr(CO)5(THF). The reaction vessel was evacuated, and then the Et2AIPPh2solution was added to the stirred Cr(CO),(THF) solution. After 14 h the solvent was removed by vacuum distillation. The resultant brown-yellow oil was dissolved in 8 mL of toluene, and the solution was filtered from unreacted Cr(C0)6 and a small amount of black solid. The volatile components were removed under high vacuum for 18 h. Attempts to crystallize the brown-yellow oil from toluene/hexane or hexane were unsuccessful. 'H N M R (toluene-d8): T 2.61 (m, Ph), 2.98 (m, Ph),6.39 (m, OCH2), 7.59 (m, b, PCH2),8.66 (m, CH,), 8.76 (m, AlCH2CH3), -9.96 (m, AlCH2). IR (neat, cm-I): vco 2076 (m), 1972 (m), 1908 (vs, vb).
Results and Discussion The first example of the new class of compounds in which a diphenylphosphido group bridges a transition metal and a main-group metal has been prepared and fully characterized. An apparent substitution of Cr(CO)5NMe3 by (Me3SiCH2)2A1PPh2occurs readily at room temperature in benzene solution to give good yields of the new compound Cr(C0)5[PPh2A1(CH2SiMe3)2.NMe3], a light yellow crystalline solid (eq 1). The identity of the new compound with Cr(CO)5NMe3+ (Me3SiCH2)2A1PPh2
-
Cr(CO),[PPh2A1(CH2SiMe3),-NMe3] (1) a Cr-P-A1 atom sequence has been determined by elemental analyses, infrared and 'H NMR spectral data, reaction chemistry, and an X-ray structural study. Other combinations of reagents did not lead to the formation of isolable compounds with the desired Cr-P-A1 atom sequence. Either reactions did not occur or a ligand on chromium reacted with the aluminum phosphide. For example, no reaction occurs between Cr(CO)5NMe3and Et2AlPPh2in toluene at room temperature for 12 h. Heating of this reaction mixture to 70 OC results in decomposition; Cr(CO), and Et2AlPPh2are isolated. The difference in reactivity at 25 "C between (Me3SiCH2)2AlPPh2 and Et2AlPPh2can be attributed to the observed association of the aluminum-phosphorus compounds in aromatic solvents. The successful reaction was observed for (Me3SiCH2)2AlPPh2, a monomer-dimer equilibrium m i ~ t u r e . ~In contrast, EtzAIPPhz is a dimer in benzene solution6 and both the aluminum and phosphorus atoms are coordinatively saturated and unavailable for reaction. The reactions of Cr(C0)6, Cr(CO)S(CH3CN), and Cr(CO),(THF) with organoaluminum phosphides do not give the desired compounds with a Cr-P-AI atom sequence. Instead, the labile ligand on chromium has been apparently attacked by the aluminum-phosphorus compound at the conditions required for reaction. The X-ray structural study demonstrates that the crystal consists of discrete isolated molecules of Cr(CO),[PPh,Al(CH2SiMe3)2.NMe3],separated by normal van der Waals distances. There are no abnormally short intermolecular contacts. Interatomic distances with their estimated standard deviations (esd's) are given in Table 111; angles appear in Table IV, while least-squares planes are defined in Table VI-S (supplementary data). Figure 1 shows the scheme used in labeling the atoms, while Figure 2 provides a stereoscopic view of the molecule. The (OC)&r-P portion of the structure has approximate C,, symmetry, and the (OC)$r-PPh2 system lends itself to comparison with parameters obtained for (OC)5Cr(PPh3).15 (15) Plastas, H.J.; Stewart, J. M.; Grim, S. 0.Inorg. Chem. 1973, 12, 265.
Inorganic Chemistry, Vol. 22, No. 7, 1983 1057
Cr(C0)5[PPh2A1(CH2SiMe3)2.NMe3] Table 111. Selected Interatomic Distances (A) with Esd's for (OC),Cr [ PPh, AI(CH, SiMe,),.NMe,]"
Cr-C(l) Cr-C(2) CIC(3) Cr-C(4) Cr-C(S)
(A) Distances in the Cr(CO), System 1.894 (4) C(1)4(1) 1.147 (5) 1.890 (4) C(2)-0(2) 1.142 (5) 1.847 (4) C(3)-0(3) 1.147 (5) 1.888 (4) C(4)-0(4) 1.145 (5) 1.879 (4) C(5)-0(5) 1.144 (5)
Cr-P
(B) Distances in the Cr-P-A1 System 2.482 (1) P-AI 2.485 (1)
(C) Phosphorus-Carbon (Phenyl) Distances P-C(l1) 1.844 (3) PC(21) 1.848 (3) (D) Aluminum-Carbon and Aluminum-Nitrogen Distances AI-C( la) 1.963 (4) AI-N 2.049 (3) AI-C(lb) 1.966 (4) Si(l)C(la) Si(l)-C(27) Si(l)-C(28) Si(l)-C(29)
(E) Silicon-Carbon Distances 1.865 (4) Si(2)-C(lb) 1.860 (5) Si(2)-C(30) 1.852 (5) Si(2)-C(31) 1.862 (5) Si(2)-C(32)
1.851 (4) 1.858 (4) 1.868 (5) 1.857 (4)
(F) Nitrogen-Carbon (Methyl) Distances N-C(2a) 1.477 ( 5 ) N-C(2c) 1.473 (6) N-C(2b) 1.474 (5) Carbon-carbon distances appear in the supplementary data (Table IV-S).
Table IV. Selected Angles (deg) within the (OC),Cr [ PPh,AI(CH, SiMe,),.NMe,] Molecule' (A) Angles around the Chromium Atom C( 1)-Cr-C(2) 90.33 (16) C(2)-Cr-P 94.90 (12) c ( 1)-CI-C(3) 88.11 (16) C(3)-Cr-C(4) 91.27 (16) c(1)-Cr-C(4) 93.73 (16) C(3)-Cr-C(5) 86.78 (16) C( 1)-Cr-C(5) 173.86 (16) C(3)-Cr-P 174.20 (12) C( l)-Cr-P 95.38 (12) C(4)-Cr-C(5) 89.78 (16) C(2)-Cr-C( 3) 89.70 (17) C(4)xr-P 83.90 (11) C(2)-Cr-C(4) 175.86 (16) C(5)-Cr-P 90.00 (1 1) C(2)-Cr-C(5) 86.26 (16) 0-P-AI Cr-P-C(l1) Cr-P-C(21)
(B) Angles around the Phosphorus Atom 124.64 (4) Al-P-C( 11) 104.00 (1 1) 105.99 (11) Al-P-C(21) 103.40 (11) 115.00 (11) C(11)-P-C(21) 100.84 (15)
P-AI-N P-AI-C( la) P-AI-C( lb)
(C) Angles around the Aluminum Atom 101.98 (9) N-AI-C(la) 104.21 (13) 116.58 (11) N-AI-C(lb) 107.77 (13) 108.21 (11) C(1a)-Al-C(lb) 116.62 (15)
(D) Angles at the Methylene Carbon Atoms Al-C(1a)-Si(1) 126.52 (19) Al-C(lb)-Si(2) 130.24 (20) (E) Angles around the Silicon Atoms C(27)-Si(l)-C(28) 108.85 (23) C(3O)-Si(2)-C(31) C(27)-Si(l)-C(29) 107.04 (24) C(3O)-Si(2)-C(32) C(27)-Si(l)-C(la) 112.44 (20) C(30)-Si(2)-C(lb) C(28)-Si(l)-C(29) 107.32 (23) C(31)-Si(2)-C(32) C(28)-Si(l)-C(la) 111.17 (20) C(31)-Si(2)-C(lb) C(29)-Si(l)-C(la) 109.81 (20) C(32)-Si(2)-C(lb)
107.38 (20) 108.06 (19) 108.50 (18) 106.56 (20) 111.99 (19) 114.07 (18)
(F) Angles around the Nitrogen Atom 109.06 (21) C(2a)-N-C(2b) 113.34 (24) C(2a)-N-C(2c) 110.21 (24) C(2b)-N-C(2c)
106.96 (29) 107.06 (30) 109.96 (32)
AI-N-C (2a) AI-N-C(2b) Al- N-C( 2 C)
(G) Chromium-Carbon-Oxygen Angles Cr-C(l)-O(l) 175.92 (34) Cr-C(4)-0(4) 177.10 (32) Cr-C(2)-0(2) 175.53 (34) Cr-C(5)-0(5) 175.28 (33) Cr-C(3)-O( 3) 178.15 (34)
03
(H) Phosphorus Carbon-Carbon Angles P-C(11)-C(12) 119.71 (25) P-C(21)-C(22) 122.90 (25) P-C(11)-C(16) 122.35 (26) P-C(21)-C(26) 119.59 (25) a
w
CSI
C30
Labeling of atoms in the (OC)&r[PPh2A1-(CH2SiMe3)2.NMe3]molecule (ORTEP-I1diagram; 30%ellipsoids; hydrogen atoms omitted).
Figure 1.
The equatorial Cr-CO linkages in the present com lex range from 1.879 (4) to 1.894 (4) 8,averaging 1.888 [6] -some 0.041 A longer than the axial Cr-CO linkage of 1.847 (4) A. [Analogous bond lengths in (OC)5Cr(PPh3) are Cr-CO (equatorial) = 1.867 (4) - 1.894 (4) A (average 1.880 [ l l ] A) and Cr-CO (axial) = 1.845 (4) A.] These results are all consistent with the accepted model for metal-carbonyl bonding; the longer Cr-CO (equatorial) bonds reflect the greater competition for d;electron density betwen the mutually trans pairs of equatorial ligands. Similar results are found in such molecules as Mn2(CO),oand Re2(CO)lo.17 The Cr-P bond length in (OC)5Cr[PPh2Al(CH2SiMe3)2.NMe3] is 2.482
J6
(16) Esd's on average distances etc. are enclosed in square brackets. They
are calculated via the "scatter formula" u
=
(17) Churchill, M.R.;Amoh, K. N.; Wasserman, H. J. Inorg. Chem. 1981,
1609.
(1) A, which is significantly longer than that of 2.422 (1) A found in (OC)5Cr(PPh3). The P-Cr-CO (equatorial) angles in (OC)5Cr[PPh2Al(CH2SiMe3)2.NMe3]are P-Cr-C(l) = 95.38 (12)O, P-CrC(2) = 94.90 (12)O, P-Cr-C(4) = 83.90 ( l l ) " , and P-CrC(5) = 90.00 (11)'; similar irregularities appear in (OC)&r(PPh3), where individual P-Cr-CO (equatorial) angles are 94.3 ( l ) , 96.2 ( l ) , 88.4 ( l ) , and 87.5 (1)'. The geometry about the tetrahedrally coordinated phosphorus atom is decidedly irregular: the Cr-P-A1 angle is increased to 124.64 (4)O, the two Cr-P-C angles are inequivalent [Cr-P-C(21) = 115.00 (11)O and Cr-P-C(11) = 105.99 (11)O], the AI-P-C angles are close to equivalent [AI-P-C(11) = 104.00 (11)' and AI-P-C(21) = 103.40 (11)O], and the C(ll)-P-C(21) angle is reduced to 100.84 (15)O. The phosphorus-carbon bond lengths [P-C(11) = 1.844 (3) A and P-C(21) = 1.848 (3) A (average 1.846 [3] A)] are slightly longer than those observed in triphenylphosphine (1.822-1.831 A)ls or in (OC),Cr(PPh,) (1.821 (3)-1.834 (4) A).15However, this is not general for derivatives of the diphenylphosphido ligand [e.g., P-C = 1.822 (5)-1.831 (5) A in Fe2(C0)6(p-C1)(p-PPh2)19 and P-C = 1.826 (5)-1.839 (6) A in F ~ R U ~ ( C O ) ~ ~ ( ~ - P P ~ Z ) Z I . ~ ~ The aluminum atom is in a rather distorted tetrahedral environment being bonding to the phosphido ligand, two alkyl
I-N
[E(d, - 6 ) * / ( N - 1)11/* I- I
20,
C-C-C angles appear as supplementary data (Table V-S).
(18) Daly, J. J. J . Chem. SOC.1964, 3799. (19) Taylor, N. J.; Mott, G . N.; Carty, A. J. Inorg. Chem. 1980, 19, 560. (20) Churchill, M. R.; Bueno, C.; Young, D. A. J . Orgammer. Chem. 1981, 213, 139.
1058 Inorganic Chemistry, Vola22, No. 7, 1983
Tessier-Youngs et al.
4
Figure 2. Stereoscopic view of the (OC)&r [PPh2A1(CH2SiMe3)2.NMe3] molecule, with all hydrogen atoms included (ORTEP-I1 diagram).
ligands, and an amine ligand. Two interligand angles are expanded from the regular tetrahedral value-P-Al-C( 1a) = 116.58 (11)O and C(1a)-Al-C(1b) = 116.62 (15)'; other angles (in decreasing order) are P-Al-C( lb) = 108.21 (1 l)', N-AI-C(1b) = 107.77 (13)O, N-AI-C(1a) = 104.21 (13)O, and P-AI-N = 101.98 (9)O. The aluminum-alkyl distances (AI-CH2SiMe3) are AI-C( l a ) = 1.963 (4) A and Al-C( 1b) = 1.966 (4) A; the average Al-C(sp3) distance is 1.965 [2] A, in good agreement with terminal aluminum-alkyl bond lengths reported previously.21a This suggests a covalent radius of -1.19 A for aluminum (cf. the accepted value of 1.18 A).Z1b The observed AI-P distance of 2.485 (1) 8,seems anomalously long when compared to the value predicted from radii -2.29 A, based on r(A1) = 1.19 A and r(P) = 1.10 An X-ray study2, of aluminum phosphide (Alp) provided an average AI-P bond distance of 2.367 A (zinc blende type of structure), whereas the electron diffraction of the adduct Me3AlPMe, suggests a long donor-acceptor AI-P bond distance of 2.53 (4) A. Thus, the comparison of these bond distances suggests that the AI-P bond in Cr(CO)5[PPh,Al(CH2SiMe3),.NMe3] might be best considered as a donoracce tor or a dative bond. The AI-N bond distance of 2.049 (3) also seems to be consistent with a donor-acceptor bond as expected. All other distances and angles in the molecule (cf. Table I11 and IV) seem normal. The isolation of the trimethylamine adduct Cr(CO)5[PPh,A1(CH2SiMe3)2.NMe3]might be unexpected in view of results obtained by other researchers. The organoaluminum phosphide MezAIPPhz reacts with NMe, to give the adduct Ph2PA1Me2.NMe3.5However, the amine can be removed by heating to 65 OC under vacuum. The ethyl-substituted compound Et,AlPPh, does not form a stable adduct with NMe,.6 This has been rationalized as a consequence of steric interaction as weaker but less sterically hindered bases such as OEt,, THF, and acridine reportedly produce adducts. We have tried to repeat several of these experiments4and find that the adduct Ph,PAlEt,.OEt, is not stable at room temperature under vacuum. Furthermore, the material claimed to be PhzPAlEt2.THF is not a true adduct but contains a cleaved THF molecule. The isolation of C r ( C 0 ) 5[PPh2Al(CH,SiMe,),-NMe,] indicates that steric considerations cannot be the only reason that Ph2PA1Et2-NMe3has not been isolated. Until these and other inconsistencies in the literature are resolved, it is difficult to make any useful comparisons
R
(21) Oliver, J. P. Adu. Orgammer. Chem. 1977,15, 235-271: (a) Table I1 on p 240; (b) Table I on p 238; (c) Table IV on p 249. (22) Pauling, L. "Nature of the Chemical Bond", 3rd ed.;Cornell University Press: Ithaca, NY, 1960. See Table 7-2 on p 224. (23) Wang, C. C.; Zaheeruddin, M.; Spinar, L. H. J. Inorg. Nucl. Chem. 1963, 25, 326. (24) Almenningen, A.; Femholt, L.; Haaland, A. J . Orgammer. Chem. 1978, 145, 109. (25) Smith, J. G . ;Thompson, D. T. J . Chem. Soc. A 1967, 1694.
between the properties of oligomeric organaluminum phosphides and Cr(CO)5[PPhzA1(CH2SiMe3)2.NMe3]. The reaction of a benzene solution of Cr(CO)5[PPh2Al(CH,SiMe,),.NMe,] with HBr is consistent with the proposed structure with the long aluminum-phosphorus bond. When 3 mol of HBr is consumed, the products include Cr(CO)5PPh2H,z3Br3AlNMe3,and SiMe4. The HBr probably reacts initially at the long AI-P bond to form Cr(CO),PPh,H and Br(Me3SiCH2),A1NMe3. Then the remaining 2 mol of HBr serve to cleave CH,SiMe, groups and form the observed products. Another possible site of initial reaction would be at the AI-N bond to form Cr(CO)5[PPhzA1(CH2SiMe3)2] and NMe3H+Br-. Subsequent reaction would produce Cr(CO)5[PPh,A1Br(CH2SiMe3)z-NMe3] and SiMe4. Consecutive reactions using this type of path could lead to the observed products. However, this latter path seems unlikely. There is no evidence for the intermediate formation of an insoluble ammonium salt at any stage during reaction. Furthermore, kinetic studies suggest that elimination reactions of organoaluminum compounds with Lewis bases with acidic protons are second-order reactions and require prior dissociation of preformed a d d ~ c t s . ~ ~Consequently, ,~' since NMe, is tightly bound and cannot be removed from Cr(C0)5[PPh2Al(CHzSiMe3),-NMe,] under high vacuum with gentle heating, reaction should occur preferentially by the dissociation of the abnormally long AI-P bond. The reaction between (Me3SiCHz),A1PPh, and Cr(C0)5NMe, to form Cr(CO)5[PPh2A1(CHzSiMe3)z-NMe3] in benzene solution is apparently slow on the NMR time scale. The extent of reaction can be easily followed by monitoring the 'H NMR spectrum of a reaction mixture at the normal operating temperature of the instrument as a function of time. Significant quantities of products were not observed until approximately 9 h of reaction time and elapsed for a reaction mixture, which had initial concentrations of approximately 2 M. The initial spectrum of the reaction mixture in benzene-d, was observed less than 5 min after combining the reagents and exhibited the patterns of the pure reagents. The chemical shifts of the reagents in the reaction mixture were only slightly shifted from those of the pure reagents. After 2 h, new lowintensity lines, suggestive of an intermediate or a secondary product but not the primary product, appeared in the regions expected for the N-methyl and Al-alkyl resonances. There was no apparent change in the phenyl region of the spectrum to suggest that the phosphorus was complexing the chromium.28 After 9.5 h the reaction mixture had lightened considerably in color and the spectrum showed that a significant amount of product had formed. However, the reactants had (26) Beachley, 0.T., Jr.; Tessier-Youngs, C. Imrg. Chem. 1979, 18, 3188. (27) Beachley, 0. T., Jr. Inorg. Chem. 1981, 20, 2825. (28) Horroch, W. D.; Taylor, R. C.; LaMar, G . N. J. Am. Chem.Soc. 1964, 86, 1303.
Cr(CO)S[PPh2A1(CH2SiMe3)2.NMe3]
Inorganic Chemistry, Vol. 22, No. 7, 1983 1059
not been entirely consumed. Only after 25.5 h were the major absorptions in the spectrum those which corresponded to the final product. Furthermore, the reaction mixture was very pale yellow, almost colorless. The spectrum after 72 h showed that reaction was essentially complete. There are a t least two possible substitution mechanisms that can be used to account for the surprisingly slow formation of Cr(CO), [PPh2A1(CH#iMe3)2.NMe3]. In one scheme, the dissociation of amine from Cr(CO),NMe3 would be followed by the rapid addition of the organoaluminum phosphide. This overall process might be expected to lead to the relatively rapid formation of product. An alterative scheme could involve the initial formation of complex between the Lewis acid end of the organoaluminum phosphide with a bonded carbonyl. A dissociative reaction followed by a substitution reaction at chromium, analogous to that proposed for the reactions of the metathesis catalysts29 W(C0),PPh3 and W(CO),P(~-BU)~ activated by AlBr3,could lead to the product. However, a rearrangement of the initial Lewis acid-carbonyl complex can also be envisioned to give the product. The definition of the reaction mechanism will have to await more detailed kinetic studies of the system. The reactions of Cr(C0)6, Cr(C0)5(CH3CN),and Cr(CO),(THF) with organoaluminum phosphides give rise to complexes in which attack of the labile ligand had occurred. The reaction of Cr(C0)6 with Me2AlPPh2in toluene requires high temperatures (>110 "C). The major product is a dark brown insoluble material, which has not been characterized. In addition, a very small quantity of a sticky yellow material is obtained. The infrared and 'H N M R spectra of this material suggest the formulation Cr(CO),[PPh2A1Me2]. All attempts to vary the reaction conditions to favor this substitution product have been unsuccessful. The small amount of the desired yellow compound in comparison to the large quantity of the brown material, the relatively small amount of CO generated during reaction, and the fact that all Me2A1PPh2was consumed suggest that processes other than substitution occur. Addition reactions of Me2AlPPh2across the carbonyl ligand, as depicted in eq 2, seem likely. The Cr(C0)e
+
MezAIPPh2
-[
,OAIMez
(C0)5Cr-C 'PPhz
j
(2)
I
resulting product may have polymerized or decomposed at the temperature for reaction. Similar addition reactions have been observed for LiPMe2O and Al(NMe2)331with transition-metal carbonyl complexes. The reactions of Cr(CO),(CH,CN) with MezAlPPh2or Et2AlPPh2in diethyl ether yield products in which the organoaluminum phosphide has added across the (29)
Taarit, Y.B.; Bilhou, J. L.; Lecomte, M.; Basset, J. M. J . Chem. SOC.,
Chem. Commun. 1978, 38. (30) Fisher, E. 0. Pure Appl. Chem. 1972, 30, 353. (311 . . (a) , , Petz. W.: Schmid. G. Annew. Chem.. Int. Ed. End. 1972.11.934. (b) Petz; W.. J. Orgakmet.?hem. 1974, 55, C42.
triple bond of the acetonitrile. This reaction course is suggested by the presence of an infrared band at about 1600 cm-' (u& in the products. In addition, the product from the Et2A1PPh2-Cr(CO),(CH3CN)reaction has an infrared band at 2156 cm-', which suggests that a nitrile adduct is also formed. The product from the reaction of Cr(CO),(THF) with Et2AlPPh2 has the simplest formula Cr(CO),(THF)(Et2AlPPh2). However, spectral data suggest that the T H F has been cleaved. The ease with which these reactions of Cr(C0),(CH3CN) or Cr(CO),(THF) with organoaluminum phosphides occur, i.e. room temperature, raised the question whether the chromium was somehow activating the organoaluminum phosphide by coordination. We have found that this is not necessarily the case. Organoaluminum phosphides react with CH3CN and T H F at room temperature to form products with spectral features analogous to those previously described! The combination of data suggests that the products from the Cr(CO),(CH3CN) reactions are probably Cr(CO),[PPh2C(CH3)=NAlR2] (R = Me, Et) and Cr(CO),[PPh2AlEt2.NCCH3]. The product from the Cr(CO),(THF) reaction is Cr(CO)S[PPh2(CH2)40A1Et2]. This latter compound has also been obtained by a completely different pathway, and a congener Cr(CO)S[PPh2(CH2)40A1(CH2SiMe3),], has been fully characterized, including an X-ray structural The reaction of Cr(CO),NMe, and (Me3SiCH2)2A1PPh2 indicates that monomeric organoaluminum phosphides have sufficient basicity to bind to chromium and replace NMe3. The reactions of Cr(C0)6, Cr(CO),(CH3CN), and Cr(CO),(THF) with organoaluminum phosphides suggest that the aluminum-phosphorus bond has a high propensity to undergo reactions with compounds that allow the AI-P bond to be replaced by the stronger bonds of aluminum and phosphorus to first-row elements. We plan to continue our efforts to clarify earlier work on organoaluminum phosphides and to investigate other possible routes for synthesizing their transition-metal derivatives. The extension of this work to the related gallium and indium derivatives is also in progress. Acknowledgment. This work was supported in part by the National Science Foundation (Grant CHE80-23448, to M.R.C.) and the Office of Naval Research. We wish to thank Mr. John P. Kopasz for growing crystals for this study. Registry No. Cr(CO)5[PPh2A1(CH2SiMe3)2.NMe3], 84558-22-5; (Me3SiCH2)2A1PPh2,84531-82-6; Cr(CO),NMe3, 15228-26-9;Cr, 1440-41-3;P, 1123-14-0;Al, 7429-90-5. Supplementary Material Available: Tables I-S-VI-S, showing observed and calculated structure factor amplitudes, calculated hydrogen atom positions, anisotropic thermal parameters, carbon-arbon distances, C-C-C angles, and least-squares planes (33 pages). Ordering information is given on any current masthead page. (32) Tessier-Youngs,C.; Youngs, W. J.; Beachley, 0. T., Jr.; Churchill, M. R. Organometallics, in press.
